The Gene Xpert is a
new test for tuberculosis. It can find out if a person is infected
with TB, and also if the TB bacterium of the person has resistance
to one of the common TB drugs, rifampicin.

How it works

The Gene Xpert is a machine that can detectmycobacterium
tuberculosisin a
sample of sputum. A person suspected of having TB needs to give a
sputum sample, which the health care worker than places in a small
tube. From the tube, the sample is fed into the machine, and then
biochemical reactions are started to see if the sample contains the
TB bacterium. The machine looks for the DNA specific to the TB
bacterium. If there are TB bacteria in the sample, the machine will
detect their DNA and automatically multiply it. This technique is
called PCR (polymerase chain reaction), and allows the machine to
also look at the structure of the genes. This is important to detect
if a TB bacterium has developed resistance to drugs. The DNA of the
TB bacterium is, in a way, like a long string of different colours.
If one or more of the colours change (if there is a mutation in the
DNA), then the bacterium can become resistant to certain TB drugs.
The Gene Xpert can test for resistance to one of the most common TB
drugs, rifampicin. This means that it can tell us two things: first,
whether or not a person has TB, and second, whether or not the TB
that the person has can be treated with rifampicin. The test is very
quick and only takes about two hours – much faster than the other TB
tests, which usually take at least a few days.